1. Field of the Invention:
This invention relates to the production of soda ash (sodium carbonate) from nahcolite (sodium bicarbonate).
2. Description of the Prior Art:
Large deposits of nahcolite (naturally-occurring NaHCO.sub.3) and of dawsonite (NaAl(OH).sub.2 CO.sub.3) are associated with oil-bearing shale formations located in the Piceance Creek Basin of northwest Colorado. The economics of recovering oil from these oil shale formations are generally more attractive for ventures that contemplate the concurrent recovery of one or more of the associated minerals.
Recovery procedures that are described in the literature for the exploitation of these oil-bearing formations have generally focused on the effective separation and recovery of oil, with little emphasis being given to specific procedures applicable to nahcolite and/or other mineral recovery.
The literature simply suggests that nahcolite can be leached from oil shale ore with aqueous solution or can be recovered by beneficiation as a nahcolite-rich portion of the ore.
U.S. Pat. Nos. 3,700,280, 3,779,601 and 3,779,602 disclose solution mining processes in which the nahcolite portion of the formation is leached, typically with hot water, and the leaching solution then withdrawn from the formation region before the cavity is retorted to recover the oil.
U.S. Pat. No. 3,962,403 is directed to a separation process applicable to dry-mined oil shale ore, in which the ore is first heated to effect a color change in the nahcolite and then an optical sorting technique is employed to efficaceously separate the nahcolite from the oil shale portion of the ore.
Despite general references in the literature to the recovery of nahcolite via dissolution in aqueous solution, there is nevertheless little specific information which describes procedures for recovering nahcolite from such solutions as a useful saleable product.
U.S. Pat. No. 3,113,834, although not concerned with nahcolite, describes a technique for processing crude ammonia-soda process sodium bicarbonate, in an aqueous slurry, into anhydrous dense sodium carbonate via decomposition of the bicarbonate in hot solution. The process is very energy-intensive and does not appear practical for application to nahcolite ore.
The method of the present invention provides a useful procedure for preparing high purity soda ash from nahcolite ore.